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PT6477 Datasheet(PDF) 9 Page - Texas Instruments |
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PT6477 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 14 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com Using the Inhibit Control of the PT6460 & PT6470 Series of Step-Down ISRs The PT6460 (5-V input) and the PT6470 (3.3-V input) series of integrated switching regulators (ISRs) provide step-down voltage conversion for output loads of up to 14 A. For applications that require the output voltage to be held off, these ISRs incorporate an Inhibit* control (pin 1). The Inhibit* control input can be used for power- up sequencing or whenever there is a requirement for the output voltage from the ISR to be turned off. The ISR functions normally with pin 1 open circuit, providing a regulated output whenever a valid source voltage is applied between Vin (pins 2–3) and GND (pins 5–8). When a low-level ground signal is applied to pin 1, the regulator output is turned off 2 and the input current is significantly reduced 3. Figure 4-1 shows the typical application of the Inhibit* function. Note the discrete transistor, Q1. The Inhibit* control has its own internal pull-up to Vin potential. An open-collector or open-drain device is recommended to control this input 1. The voltage thresholds are given in Table 4-1. Table 4-1; Inhibit Control Requirements Parameter Min Typ Max Enable (VIH)Vin – 0.5 V — Open Disable (VIL) –0.2 V — +0.8 V I IL — –0.2 mA — Notes: 1. Use an open-collector device with a breakdown voltage of at least 10 V (preferably a discrete transistor) for the Inhibit* control input. A pull-up resistor is not necessary. To disable the output voltage the control pin should be pulled low to less than +0.8 VDC. 2. When a ground signal is applied to the Inhibit* control (pin 1) the module output is effectively turned off (tri- state). The output voltage decays to zero as the load impedance discharges the output capacitors. 3. When the output is disabled via the Inhibit* pin, the input current is reduced to approximately 5 to 10 mA. Figure 4-1 Turn-On Time: In the circuit of Figure 4-1, turning Q1 on applies a low-voltage to the Inhibit* control (pin 1) and disables the output of the regulator 2. If Q1 is then turned off, the ISR executes a soft-start power up. Power up consists of a short delay (approx. 2 msec), followed by a period in which the output voltage rises to the full regu- lation voltage. The module produces a regulated output voltage within 10 msec. Figure 4-2 shows the typical rise in both the output voltage and input current for a PT6464 (1.8 V), following the turn-off of Q1. The turn off of Q1 corresponds to the rise in the waveform, Q1 Vds. The waveforms were measured with a 5VDC input voltage, and 8.5-A load. Figure 4-2 Vo (1V/Div) Iin (2A/Div) Q1Vds (5V/Div) HORIZ SCALE: 2ms/Div PT6460 & PT6470 Series C IN 560 µF (Req'd) COM +V IN + PT6464 2–4 5–812 9–10 Vin Vout Vo(adj) GND 1 Inhibit* C OUT 330 µF (Optional) +Vsense + 11 1 =Inhibit Q 1 BSS138 L O A D GND V OUT +V SENSE |
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